The present invention relates generally to glass forming and particularly to a method and apparatus for altering the temperature of mold equipment such as forming molds and plungers, especially those plungers with narrow long portions requiring increased heat removal.
Glass articles are customarily formed by placing a charge of hot molten glass into a mold cavity and then introducing a plunger into the charge of glass so as to press-form a finished article between the mold and the plunger. A major consideration in this forming process is the control of heat distribution and removal of heat in order that the surfaces which form the glass articles are neither too hot nor too cold. The repeated exposure of the mold and plunger, as they come into contact with the molten glass during the forming operation, causes the temperatures thereof to rise, and therefore it is imperative that they be cooled to within acceptable working ranges. If, for example, the mold is not cooled sufficiently, it will reach a temperature at which the glass will begin to fuse to the metal interior forming surface of the mold; which, necessitates the stoppage of the forming equipment in order to repair the damage caused by the fusing. If the temperature of the mold is not maintained, or if permitted to fall below a predetermined level, wrinkles, checks and other imperfections can result in the finished article.
The problem of maintaining the mold equipment within a limited temperature range during various production speeds is aggravated by differential rates of heat removal from the mold equipment which occurs with articles exhibiting certain unique types of geometries. Furthermore, the rate of heat removal from the molten glass by the mold equipment depends to a large extent on the glass thickness and its geometric shape in localized regions. If the glass item to be produced has regions of both broad flat or slightly curved surfaces and also regions of relatively sharp corners, the rate of heat exchange between the glass and the mold equipment can differ significantly from one region to the next. Under such circumstances the conventional cooling systems for plungers used in glass pressing are inadequate for handling differential cooling rates in adjacent regions or zones because present methods of cooling plungers involved in a single source of cooled fluid entering the plunger in one single chamber. This single source of cooling fluid thereafter flowed via random motion to various locations and generally collected at a single location with resultant individually varying return flow paths which affect one another causing arbitrary and undesirable side effects in the cooling system design and in plunger thermal performance.
One such solution to single-source single-collection problem of cooling is disclosed in related patents U.S. Pat. No. 4,059,429 (Carmi et al.) and U.S. Pat. No. 4,094,657 (Carmi et al.); a differentially cooled plunger apparatus and a method of differentially cooling a plunger respectively. In general, these patents disclose a plunger and the use of a plunger designed in such a manner that a single-source cooling fluid is supplied to different zones or regions of the plunger for differential cooling of the zones or regions; specifically, the regions possessing sharp curvatures and requiring high heat removal and regions possessing lesser curvatures requiring lesser heat removal.
Although the above described Carmi patents disclose methods of press-forming designed for supplying differential cooling to areas where differential heat removal is necessary, the method and the apparatus is not geometrically suitable for use in the formation of articles which exhibit long, narrow protuberances, i.e., specifically, those type of products which may be found in the lighting industry which incorporate sharp angles and/or narrow, long "noses". The large area required for the prior art baffle, plenum chamber and the plurality of cooling fluid passages makes the aforementioned prior art method of differential cooling unsuitable in those molding configurations having narrow plungers or nose portions which require a differential heat removal rate when compared to the rest of the plunger portion.
This being the case, the need remains for a high production method and apparatus for press-forming glass articles which exhibit geometries possessing long, narrow protuberances.